1. Field of the Invention
The present invention relates to a method of using atomic absorption spectroscopy to accurately measure atomic beam flux rate in a vacuum chamber of an apparatus used to grow films, such as a molecular beam epitaxy (MBE) apparatus, a vacuum deposition apparatus, an ion beam deposition apparatus, a laser ablation film fabrication apparatus and a sputter deposition apparatus.
2. Description of the Prior Art
Measurement of atomic beam flux rate in a vacuum chamber of an apparatus used to grow films such as an MBE apparatus, vacuum deposition apparatus, ion beam deposition apparatus, laser ablation film fabrication apparatus, sputter deposition apparatus and the like is important with respect to controlling thin-film fabrication. Atomic absorption spectroscopy (AAS) makes it possible to measure flux rate regardless of the state of the atoms (discrete, molecule or cluster particle, or ionized states thereof). Measurement of beam flux rate in thin-film fabrication apparatuses has been extensively utilized, with a hollow cathode lamp used as the spectral light source.
In a conventional AAS system using a hollow cathode lamp, constant-intensity light emitted by the hollow cathode lamp is interrupted by a mechanical chopper, detected by a photodetector, and the output of the photodetector is locked-in using a lock-in amplifier. Such a system is described, for example, in "MBE Growth of BiSrCaCuO Films Using Flux Monitoring by Atomic Absorption Spectroscopy," by Y. Kasai, A. Suzuki, H. Tanoue, T. Nagai and S. Sakai, (Advances in Superconductivity (vol. 7 (1995) pp. 897-900), and "Accurate measurement of atomic beam flux by pseudo-double-beam atomic absorption spectroscopy for growth of thin-film oxide superconductors," by M. E. Klausmeier-Brown, J. N. Eckstein, I. Bozovic and G. F. Virshup (Applied Physics Letter vol. 60 (1992) pp. 657-659).
However, a problem with the above method in which a mechanical chopper is used is that the magnetic field generated by the motor used to drive the chopper has an adverse effect on observation of the crystal surface using an electron beam, such as in reflection high-energy electron diffraction (RHEED), destabilizing the RHEED image. Another problem is that of vibration produced by the mechanical parts, while a further problem is that the size of the chopper disks imposes constraints on the disposition of the parts making up the optical system, and using a chopper increases the cost of the apparatus.
The object of the present invention is to provide a method of accurately measuring beam flux rate in a vacuum chamber of an apparatus used to grow films, using atomic absorption spectroscopy, without employing a mechanical chopper.